1. Field of the Invention
This invention relates to recording members for information recording by means of high energy density light beams, such as a laser light beam.
2. Description of the Prior Art
In addition to light-sensitive members such as those based on silver salts, recording members in which information is recorded using high energy density beams e.g., of an energy sufficient to thermally deform, such as a laser, include heat-sensitive recording members as described below. Heat-sensitive members for recording using high energy density light beams have a recording layer with a high optical density for the high energy density light beam to be used. When the beam impinges onto such a recording layer, a localized increase in temperature takes place to cause thermally initiated phase changes or thermally initiated structure changes such as melting, vaporization, aggregation, etc. to occur. Such changes lead to a removal of the recording layer at the irradiated area, which gives rise to an optical density difference between the irradiated area and the non-irradiated area to record information. Such types of heat-sensitive recording members have various advantages such as the elimination of additional processings such as development, fixation, etc., the elimination of the necessity for use of a dark room due to lack of sensitivity to normal room illumination, the capability of forming an extremely high contrast image, the ability to subsequently record additional information, i.e., add-on capability, etc.
In most of the cases where information is recorded onto such heat-sensitive members, the information to be recorded is usually converted into the form of an electrical, time-sequential signal, depending on how the intensity of the laser beam is modulated. The recording member is scanned with the modulated beam whereby a permanent image is obtained simultaneously with the recording, in other words, a real time recording is accomplished.
The recording layer for such heat-sensitive recording members can generally comprise inexpensive materials including metals, dyes, plastics, etc. Such recording members are described, for example, in the proceedings of the 11th Symposium on Electron, Ion & Laser Beam Technology edited by M. L. Lenene et. al. (1969), Electronics p.50 (1968), D. Maydan The Bell System Technical Journal, Vol.50 p.1761 (1971), C.O. Carlson Science, Vol.154 p.1550 (1966), etc. Metal based recording layers, consisting of a thin coating of Bi, Sn, In, etc., are prominent as heat-sensitive recording member due to their high resolving power as well as the extremely high contrast of the recorded image. However, many such recording members cannot efficiently make use of laser energy due to a loss caused by a relatively large surface reflectance, which often exceeds 50%, of the recording member. This inevitably leads to an increase in the recording energy of the light beam. Therefore, to ensure a high scanning rate in recording, a very high power laser source is required. As a result, the overall recording apparatus becomes bulky and expensive. As a matter of course, recording members with higher recording sensitivity have been investigated. One example described in U.S. Pat. No. 3,560,994 utilizes a multi-layer structure comprising Se, Bi and Ge. In this structure, the light reflectance of the thin coating comprising Se and Bi is reduced by overlaying a very thin coating of Ge on the Se and Bi layer. Two drawbacks are evident in this approach; one is the use of Se which is toxic, and the other is the poor quality of the recorded images.
Japanese Patent Application (OPI) 74632/1976 describes recording members of another type provided with a reflection preventing layer on the metal recording coating, this reflection preventing layer exhibiting an intense absorption at the wavelength of the laser light used for recording. Such a reflection preventing layer, however, cannot eliminate reflection completely. Even if one could succeed in a complete elimination of surface reflection, still a high power source for the laser is required to cause phase or structure changes such as melting, evaporation, aggregation, etc. in a thin metal layer. Therefore, recording members with a much higher recording sensitivity have been desired for a long time.